Breast cancer anti-estrogen resistance protein 1 is a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
that in humans is encoded by the ''BCAR1''
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
.
Gene
BCAR1 is localized on chromosome 16 on region q, on the negative strand and it consists of seven exons. Eight different gene isoforms have been identified that share the same sequence starting from the second
exon
An exon is any part of a gene that will form a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term ''exon'' refers to both the DNA sequence within a gene and to the corresponding sequen ...
onwards but are characterized by different starting sites. The longest isoform is called BCAR1-iso1 (RefSeq NM_001170714.1) and is 916 amino acids long, the other shorter isoforms start with an alternative first exon.
Function
BCAR1 is a ubiquitously expressed adaptor molecule originally identified as the major substrate of
v-Src
v-Src is a gene found in Rous sarcoma virus (RSV) that encodes a tyrosine kinase that causes a type of cancer in chickens.
The src gene is oncogenic as it triggers uncontrolled growth in abnormal host cells. It was the first retroviral oncogen ...
and
v-Crk . p130Cas/BCAR1 belongs to the
Cas family of
adaptor proteins and can act as a docking protein for several signalling partners.
Due to its ability to associate with multiple signaling partners, p130Cas/BCAR1 contributes to the regulation to a variety of signaling pathways leading to
cell adhesion
Cell adhesion is the process by which cells interact and attach to neighbouring cells through specialised molecules of the cell surface. This process can occur either through direct contact between cell surfaces such as cell junctions or indir ...
,
migration
Migration, migratory, or migrate may refer to: Human migration
* Human migration, physical movement by humans from one region to another
** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...
, invasion,
apoptosis
Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes incl ...
,
hypoxia
Hypoxia means a lower than normal level of oxygen, and may refer to:
Reduced or insufficient oxygen
* Hypoxia (environmental), abnormally low oxygen content of the specific environment
* Hypoxia (medical), abnormally low level of oxygen in the tis ...
and mechanical forces. p130Cas/BCAR1 plays a role in cell transformation and cancer progression and alterations of p130Cas/BCAR1 expression and the resulting activation of selective signalling are determinants for the occurrence of different types of human tumors.
Due to the capacity of p130Cas/BCAR1, as an adaptor protein, to interact with multiple partners and to be regulated by
phosphorylation
In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, wh ...
and
dephosphorylation
In biochemistry, dephosphorylation is the removal of a phosphate (PO43−) group from an organic compound by hydrolysis. It is a reversible post-translational modification. Dephosphorylation and its counterpart, phosphorylation, activate and deac ...
, its expression and phosphorylation can lead to a wide range of functional consequences. Among the regulators of p130Cas/BCAR1 tyrosine phosphorylation,
receptor tyrosine kinase
Receptor tyrosine kinases (RTKs) are the high-affinity cell surface receptors for many polypeptide growth factors, cytokines, and hormones. Of the 90 unique tyrosine kinase genes identified in the human genome, 58 encode receptor tyrosine kinase ...
s (RTKs) and
integrin
Integrins are transmembrane receptors that facilitate cell-cell and cell-extracellular matrix (ECM) adhesion. Upon ligand binding, integrins activate signal transduction pathways that mediate cellular signals such as regulation of the cell cycle, ...
s play a prominent role. RTK-dependent p130Cas/BCAR1 tyrosine phosphorylation and the subsequent binding with specific downstream signaling molecule modulate cell processes such as actin
cytoskeleton
The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is compos ...
remodeling, cell adhesion, proliferation, migration, invasion and survival.
Integrin
Integrins are transmembrane receptors that facilitate cell-cell and cell-extracellular matrix (ECM) adhesion. Upon ligand binding, integrins activate signal transduction pathways that mediate cellular signals such as regulation of the cell cycle, ...
-mediated p130Cas/BCAR1 phosphorylation upon adhesion to
extracellular matrix
In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide stru ...
(ECM) induces downstream signaling that is required for allowing cells to spread and migrate on the ECM.
Both RTKs and integrin activation affect p130Cas/BCAR1 tyrosine phosphorylation
and represent an efficient means by which cells utilize signals coming from growth factors and integrin activation to coordinate cell responses. Additionally, p130Cas/BCAR1 tyrosine phosphorylation on its substrate domain can be induced by cell stretching subsequent to changes in the rigidity of the extracellular matrix, allowing cells to respond to mechanical force changes in the cell environment.
Cas-Family
p130Cas/BCAR1 is a member of the Cas family (Crk-associated substrate) of adaptor proteins which is characterized by the presence of multiple conserved motifs for protein–protein interactions, and by extensive tyrosine and serine phosphorylations. The Cas family comprises other three members:
NEDD9
Neural precursor cell expressed developmentally down-regulated protein 9 (NEDD-9) is a protein that in humans is encoded by the ''NEDD9'' gene. NEDD-9 is also known as enhancer of filamentation 1 (EF1), CRK-associated substrate-related protein (CA ...
(Neural precursor cell expressed, developmentally down-regulated 9, also called Human enhancer of filamentation 1,
HEF-1 or Cas-L),
EFS (Embryonal Fyn-associated substrate), and
CASS4
Cas scaffolding protein family member 4 is a protein that in humans is encoded by the CASS4 gene.
History and discovery
CASS4 (Crk associated substrate 4) is the fourth and last described member of the CAS protein family. CASS4 was detected by ...
(Cas scaffolding protein family member 4).
These Cas proteins have a high structural homology, characterized by the presence of multiple protein interaction domains and phosphorylation motifs through which Cas family members can recruit effector proteins. However, despite the high degree of similarity, their temporal expression, tissue distribution and functional roles are distinct and not overlapping. Notably, the knock-out of p130Cas/BCAR1 in mice is embryonic lethal, suggesting that other family members do not show an overlapping role in development.
Structure
p130Cas/BCAR1 is a scaffold protein characterized by several structural domains. It possesses an amino
N-terminal
The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the ami ...
Src-homology 3 domain (SH3) domain, followed by a proline-rich domain (PRR) and a substrate domain (SD). The substrate domain consists of 15 repeats of the YxxP consensus phosphorylation motif for Src family kinases (SFKs). Following the substrate domain is the serine-rich domain, which forms a four-helix bundle. This acts as a protein-interaction motif, similar to those found in other adhesion-related proteins such as focal adhesion kinase (FAK) and vinculin. The remaining carboxy-terminal sequence contains a bipartite Src-binding domain (residues 681–713) able to bind both the SH2 and SH3 domains of Src.
p130Cas/BCAR1 can undergo extensive changes in tyrosine phosphorylation that occur predominantly in the 15 YxxP repeats within the substrate domain and represent the major post-translational modification of p130Cas/BCAR1. p130Cas/BCAR1 tyrosine phosphorylation can result from a diverse range of extracellular stimuli, including growth factors, integrin activation, vasoactive hormones and peptides ligands for G-protein coupled receptors. These stimuli triggers p130Cas/BCAR1 tyrosine phosphorylation and its translocation from cytosol to the cell membrane.
Clinical significance
Given the ability of p130Cas/BCAR1 scaffold protein to convey and integrate different type of signals and subsequently to regulate key cellular functions such as adhesion, migration, invasion, proliferation and survival, the existence of a strong correlation between deregulated p130Cas/BCAR1 expression and cancer was inferred. Deregulated expression of p130Cas/BCAR1 has been identified in several cancer types. Altered levels of p130Cas/BCAR1 expression in cancers can result from gene amplification, transcription upregulation or changes in protein stability. Overexpression of p130Cas/BCAR1 has been detected in human breast cancer, prostate cancer, ovarian cancer, lung cancer, colorectal cancer, hepatocellular carcinoma, glioma, melanoma, anaplastic large cell lymphoma and chronic myelogenous leukaemia.
The presence of aberrant levels of hyperphosphorylated p130Cas/BCAR1 strongly promotes cell proliferation, migration, invasion, survival, angiogenesis and drug resistance.
It has been demonstrated that high levels of p130Cas/BCAR1 expression in breast cancer correlate with worse prognosis, increased probability to develop metastasis and resistance to therapy.
Conversely, lowering the amount of p130Cas/BCAR1 expression in ovarian, breast and prostate cancer is sufficient to block tumor growth and progression of cancer cells.
p130Cas/BCAR1 has potential uses as a diagnostic and prognostic marker for some human cancers. Since lowering p130Cas/BCAR1 in tumor cells is sufficient to halt their transformation and progression, it is conceivable to propose p130Cas/BCAR1 may represent a therapeutic target. However, the non-catalytic nature of p130Cas/BCAR1 makes difficult to develop specific inhibitors.
Notes
References
Further reading
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External links
Bcar1Info with links in th
Cell Migration Gateway*
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{{PDB Gallery, geneid=9564
Proteins